The invention concerns a two-stroke engine, in particular, for a hand-guided working tool such as a motor chainsaw, a cut-off machine or the like. The two-stroke engine comprises a cylinder in which a combustion chamber is disposed that is delimited by a reciprocating piston. The piston drives by means of a connecting rod a crankshaft rotatably supported in a crankcase. The crankcase, in predetermined positions of the piston, is connected by at least one transfer channel to the combustion chamber. The engine further comprises a mixture channel for supplying a fuel/air mixture and an air channel that supplies substantially fuel-free air to the transfer channel.
U.S. Pat. No. 6,450,135 B1 discloses a two-stroke engine that supplies substantially fuel-free air to the transfer channels arranged near the exhaust port. The substantially fuel-free air serves for scavenging the exhaust gas from the combustion chamber. The air that is contained in the transfer channels must be matched to the supplied quantity of fuel/air mixture. The supplied fuel quantity can be adjusted conventionally by means of an adjusting screw of a carburetor. In order to match the supplied air quantity to the operational state of the internal combustion engine, a throttle valve can be provided in the air channel.
The flow cross-section of the air channel is very small in two-stroke engines of small piston displacement. Mounting of the throttle valve is difficult in such a small channel. Since for different two-stroke engines different flow cross-sections of the air channel are required, it is necessary to provide air channels with different flow cross-sections for a cylinder model range with different piston displacements. This requires a significant expenditure in regard to tools for manufacturing the air channels as well as for stockholding the different channels.